The invention relates to an arrangement for the accurately positioned quick-action clamping and tensioning of printed plates on a plate cylinder of a printing machine.
In such a machine, the cylinder carries front and rear tensioning bars each having a clamping device for clamping a printing plate. Camshafts are associated with the clamping devices and, upon being rotated, are operable to actuate the clamping devices.
An arrangement of this general type is known from DE-PS 3 516 682 and, in a known manner, allows the printing plate to be clamped at the start and end of the print by turning of the camshafts associated with the corresponding tensioning bars, using a manually actuated tool. Subsequent tensioning of the printing plate is then also carried out manually by means of a tool, the tensioning bar at the print end being moved from the rear gap wall substantially circumferentially by way of a central actuating device and a pressure strip. A disadvantage of this system is that a number of manual operations are required at the cylinder gap and automatic retensioning during machine operation is not guaranteed.
DE-OS 3 843 433 describes a system for the quick-action tensioning of printing plates, the camshafts which effect clamping and tensioning being provided with double cam followers at each of the cylinder side walls and being turnable, for clamping, unclamping, tensioning, and releasing, via an actuating device fixed to the frame, after the plate cylinder has been positioned to the appropriate angle.
A technically similar way is also described by EP-A2 0 260 492, in which the camshafts at the cylinder side walls carry single lever arms instead of double lever arms and are turnable by tension or pressure via an actuating device on the frame side.
A disadvantage of both solutions is that tensioning of the printing plate can be carried out only in a specific position of the plate cylinder and there is no guarantee of re-tensioning during operation of the machine, and particularly there is no guarantee of automatic retensioning. There are also negative effects on the clamping and tensioning state due to the double or single levers which also rotate and also require room, and this is due particularly to the impacts as the plate gap and the blanket cylinder gap roll on and off one another.
Another system for accurately positioned quick-action tensioning is shown in DE-OS 3 843 395. According to this, at least one common actuating device disposed on the machine front is associated with the clamping and tensioning system, such actuating device corresponding to the angular position of the plate cylinder at the time of clamping and tensioning. Clamping and tensioning are effected via axially movable draw key transmissions which are movable by the actuating devices disposed on either side of the cylinder side walls. Here again tensioning is not possible during machine operation. Another disadvantage is that the forces for clamping, unclamping, tensioning and releasing always act axially and must therefore be taken by the plate cylinder bearings.